The present disclosure relates in part to isolated or recombinant nucleic acids encoding PUFA-PKS systems, to genetically modified microorganisms comprising such PUFA-PKS systems, and to methods of making and using such microorganisms that include heterologous PUFA-PKS systems.
Polyunsaturated fatty acids, or PUFAs, are fatty acids that contain more than one double bond in their backbone. Long-chain polyunsaturated fatty acids, including those of the omega-3 family, are an essential part of the human diet. They are important constituents of phospholipids that play a role in decreasing membrane rigidity. In particular, eicosapentaenoic acid (EPA) serves as a precursor of prostaglandins and resolvins. Another important PUFA of the omega-3 family is docosahexaenoic acid (DHA). Improved cognitive and behavioral function in infant development seems correlated to high levels of this compound. For omega-3 PUFAs, and in particular for DHA and EPA, beneficial health effects have been shown e.g. the prevention of cancer, rheumatoid arthritis, cardiovascular diseases, the improvement of immune function, and eye and brain health.
Presently, fish oil is the most abundant and widely used natural source for omega-3 fatty acids. Due to problems with overfishing as well as heavy metal contamination of fish stocks, there is a need for an alternative and sustainable source of PUFAs.
Various groups of marine algae have been explored for over 20 years and some products based on algal biomass have meanwhile entered the market. Some oomycetes belonging to the group of stramenopiles were also occasionally reported to produce the above mentioned compounds, e.g. of the genera Achyla and Pythium. In other stramenopiles, e.g. the genera Schizochorium and Thraustochytrium, DHA may represent up to 48% of the fatty acid content of the cells, which are the highest contents so far known in the Eukaryota. Other alternative biological sources for omega-3 PUFAs are prokaryotic eubacteria. However, the commercial exploitation of these organisms for PUFA production on an industrial scale is hampered by the slow growth characteristics of these psychrophilic bacteria, as well as their inherently low yields and productivity.
It has been established that PUFAs are biosynthesized in a similar manner as the polyketide secondary metabolites in both prokaryotic and eukaryotic organisms. Gene clusters encoding synthetic pathway enzymes for biosynthesis of omega-3 PUFAs have been documented for various marine bacteria, including species of the genera Moritella, Photobacterium, and Shewanella. Heterologous expression of a polyketide synthase gene cluster from Shewanella oneidensis MR-1 is reported to result in the production of EPA in E. coli cultured at 15° C. (Lee et al. Biotech. Bioproc. Eng. 11, 510-515, 2006). DHA has been synthesized by E. coli by expression of a gene cluster from Moritella marina MP-1 (Orikasa et al. Biotechnol. Lett. 28, 1841-1847, 2006).